Katie Jarvis - Essex's accidental actress

Katie Jarvis followed the critical acclaim of Fish Tank with awards, more film offers and a baby daughter. She tells Charlotte Cripps that she finds her life increasingly surreal for a teenager

Katie Jarvis made quite a splash with her first ever acting role in Fish Tank. A month ago, the 18-year old actress crowned a spectacular 2009 by winning the Best Newcomer prize at the British Independent Film Awards (Bifas) for her starring role as the mouthy Mia.

In the film, which is released on DVD at the end of this month, she plays a troubled teenager who has a difficult relationship with her uncaring mother (played by Kierston Wareing), but finds solace in practising hip-hop dance moves in an abandoned flat, and fantasising about her mum's boyfriend (Michael Fassbender). She celebrated her 18th birthday in June at the Edinburgh International Film Festival, where Sean Connery presented her with the Trailblazer award, along with a bunch of lilies and a birthday cake, and she went on to win Best Performance in a British Feature Film.

Since then, she has been nominated for Best Actress at the European Film Awards, which pitted her against such established movie stars as Kate Winslet and Penelope Cruz, and has won the Pinewood Studios Best Performance Award at the Woman in Film and TV Awards (WFTV) where she was joined by Helen Mirren.

And she has hung out with fellow newcomer sensation Carey Mulligan, who stars in An Education, at the Telluride Film Festival in Colorado, where they were interviewed together on stage by Leonard Maltin.

"I felt like it came quite naturally" , says Jarvis of her first film role. "The more it went on, the more I enjoyed it. When I first went into it, I didn't know anything at all about the film industry". Jarvis said her guidance has come from the director of Fish Tank, Andrea Arnold. "If it wasn't for Andrea... then I wouldn't be here today. Definitely not." Her co-star Fassbender (Hunger and Inglourious Basterds), with whom she shared a challenging sex scene, has said of the newcomer: "Katie is a very expressive person and very easy to play with as she's not really acting".

Now Jarvis has been snapped up by the same Hollywood agent as Johnny Depp and, contrary to reports that she doesn't want to continue acting, is determined to get as much mileage out of films as possible. She's currently auditioning for the part of Richard Gere's daughter in The Flim-Flam Man and has just landed a small part in another feature film, The Big Splash, as a young girl followed by a conman who is pretending to be a casting agent for a model agency. She was up to play a female thug in Harry Brown opposite Michael Caine, another mouthy part, but couldn't do it because she was pregnant. She has turned down parts too, including in Shank, a sort of futuristic Kidulthood, because she doesn't want to get typecast as a volatile teenager. "I don't want to be pigeonholed as the stroppy teenager. I'm not Mia – so I don't want to play her all the time."

Jarvis grew-up in Dagenham with her parents, Paul, a painter and decorator, and Tamara, a housewife, who divorced when she was 12. Her three younger sisters, Charmaine, 16, Jodie-May, 13, and Beckie, 11, have all watched in amazement as their sister went on to feature-film stardom overnight. Jarvis says her own background was very different from Mia's, whose life is relentlessly hard. "I'd always been taught not to scream and swear and shout back," she says. "So for me it was fun acting Mia."

She left school with six GCSEs and was planning to take hair and beauty and IT courses at her local college before she was plucked from obscurity to star in Fish Tank. A casting director discovered her at 16, while she was having an argument on Tilbury Town train station with her boyfriend, Brian Hanlon. "If this has happened to me, then anything can happen to anyone", she says in a polite Essex twang. "You never know what's around the corner,"

The slim actress is sitting in the Curzon Soho cinema in London, still wearing her coat and eating a sandwich. "It's nuts. Do you know what I mean? A lot of people think what's happened to me is surreal. It doesn't seem real sometimes. It feels like a dream."

Although she has stunned fans and critics with her debut performance in Fish Tank, Jarvis appears under-confident as she talks about keeping her fingers crossed for new parts. "I don't think the film will change me. I think it might make me a better person. Acting brings out the best in me. Before Fish Tank I was at school and didn't have the guts to do drama. This has boosted my confidence right up."

Arnold, who won the Cannes Jury Prize in 2006 for her debut feature Red Road, had initially looked to cast a trained dancer in the role of Mia, but she couldn't find anybody right. Then when Jarvis turned up for her audition, she refused to dance for it. "We had to leave the camera in the room and go out. She hates dancing," said Arnold.

It is surprising Jarvis even made it to the audition in the first place. She thought it was some kind of joke when the casting agent discovered her on the train platform.

"There weren't a lot of people at the first audition so I wasn't nervous, but at the second it became a bit more scary as there were a lot of girls. I'd never done any dancing or anything like that and I didn't think I had a chance."

During filming, Rashad Omar, the sound recordist, said of Jarvis: "I thought she would walk after a week. It's amazing how she picked it up."

Her only downfall during filming was her penchant for new shoes, and balancing work and play. "When you've done film before, you know how to pace yourself at the weekend," said Arnold. "But Katie'd go out and party or buy loads of shoes with the money that she suddenly had."

It was a demanding shoot, thanks in no small part to a sex scene with Fassbender for which she had little time to prepare. "Andrea made me aware from the start that there was going to be a sex scene. But I didn't know who it was with, because she doesn't let the cast read ahead in the script," says Jarvis. "I only found out the night before that it was going to be with Michael. I was up all night feeling absolutely terrified, but Michael made it easy for me. He turned it into a laugh and a joke. It was as though it was like any other scene we had done. He is so down-to-earth, funny and easy to get on with."

Since Fish Tank she has played the young mother in a 10-minute silent film, Perfect Day, with the Skins actor Merveille Lukeba. It aired in December on Sky as part of a collection of short films, "Ten Minute Tales", which also starred Bill Nighy and Natascha McElhone.

Otherwise she has been keeping a low profile because, just four days before Fish Tank premiered at the Cannes Film Festival in May, she gave birth to her daughter, Lillie-May. Lately Jarvis's life has revolved around feeding the ducks with Lillie-May, now nine months old, near the two-bedroom rented flat in Basildon that she shares with her boyfriend .

She watched online as her co-stars posed on the red carpet at Cannes because she didn't want to leave her newborn baby. At the time, Arnold said of Jarvis: "I don't think she really understands what this means. Festivals and things are not really part of her life."

Still, she entered the limelight with a bang at the Bifas just before Christmas when, in a long black Armani dress, she joined director Arnold, who also won Best Director for the film at the ceremony. "I'm so happy, I can't believe it," Jarvis said. "A long time ago I didn't think I would end up here. I'm speechless. I don't know what to say."

Now Jarvis says she's never happier than when she is in front of the camera. "I have never enjoyed myself as much as I have acting. Nothing compares to it," she says. "Everybody gets so close on set. It's like a little family unit. It's horrible to then say goodbye. But it's lovely at the end of it to have something to look at that we've all done together."

However, Arnold didn't think her new star had the acting bug after Fish Tank. "She has got an agent and she's been up for a couple of things and got them but I don't know whether she wants to continue. I think she does but she's just had a baby and that's a whole other life."

But this couldn't be further from the truth, as Jarvis is impatient to conquer the film industry, with the help of her boyfriend, who will have to play househusband and look after their baby.

"Before I was doing nothing all the time. It made me learn that I could do things if I wanted to. Now I want to make the most of it. It shows you don't have to go to drama school to get into it, but I think I was one of a kind. I don't think anyone else will get picked off a train station."

'Fish Tank' is out on DVD on 25 January